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Sujet de stage / Master 2 Internship

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Dynamics of water confined in hydrophobic materials

Contact: ALBA-SIMIONESCO Christiane, , christiane.alba-simionesco@cea.fr, +33 1 69 08 32 54
Summary:
The properties of confined liquid water not only differ from those of bulk water but also greatly vary one from another depending on the confinement characteristics. The variety comes from the interplay between the rich water phase diagram and the length and time scales involved on one side and the wide diversity of confining conditions, size and dimension of the matrix, softness and roughness of its surface, nature of the interactions, etc., on the other. The list of confining situations is broad and generically includes all cases where water molecules are trapped in a given environment, provided the environment and the water evolve on widely different time scales. Here we focus on water confined in solid and regular materials, with pore sizes allowing mobility and phase transitions from the liquid state. The advantage of the synthesis route we have chosen is the possibility to tune the hydrophobicity of the surface from weakly to very hydrophobic in a well-controlled way for pore diameters ranging from 2.5 to 5nm.
Possibility of continuation in PhD: Oui
Deadline for application:28/02/2023

Full description:
A lot of experiments on confined water have already been performed and many controversial results can be found in the literature. Here we would like to focus on new features observed because of the use of an external pressure at variance to standard experiments which modify the amount of water trapped between the walls. In particular the local thermodynamic properties, the temperatures of the phase transitions will be affected in a non-trivial way, giving rise to the observation of new crystalline phases (ref 1) in unexpexted T-P domains. Several situations must then be considered since the ingress of a liquid into a nanoporous material depends not only on the dimension of the pores but also on the interactions between the liquid and the material surfaces. In the case hydrophilic pores, the filling process is called imbibition, when penetration started as soon as the materials are in contact with the liquid, or, in the hydrophobic case, intrusion(ref 1) when an external pressure is required to force the liquid to enter, with a pressure value obeying the Laplace law. In all cases the kinetics of in and out are different and the time scale of equilibration very long.
Technics/methods used during the internship:
Materials characterization : Adsorption N2 Water, SAXS, FTIR, TGA. Confined fluid studies: WAXS, Neutron Scattering (elastic and quasielastic), calorimetry.

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